The present invention relates generally to an electronic system circuit package, and more particularly to a package including a lead frame having a unique and specific design with provisions for electrically interconnecting a plurality of passive and active electronic components, at least in part directly by means of the lead frame in accordance with a specific predetermined circuit design.
In integrated circuit packaging, a lead frame is typically used to support an integrated circuit within an integrated circuit package as well as to provide electrically conductive leads for the connection of the integrated circuit to other circuit elements outside the package. To date, as a general rule only the integrated circuit itself has been mounted directly to the lead frame within the integrated circuit package, while other cooperating components have typically been placed outside the package. This segregation of components leads to a multiplicity of problems encountered in circuit design which problems are solved by the present invention, also to be discussed below.
A past solution was to include some components within the integrated circuit package by mounting those components to a dielectric substrate which was then, in turn, mounted to the lead frame. This prior art method introduces an additional layer of thermal impedance from the parts mounted on the substrate to the lead frame, since the substrate is typically a poor thermal conductor as compared with metal lead flames. As will be seen hereinafter in accordance with the present invention, mounting and electrically connecting parts directly to the lead frame avoids the need for a substrate. Components mounted directly to the lead frame will exhibit improved heat dissipation characteristics since the metal lead frame is an efficient conductor of heat. Higher manufacturing costs and complexity will also be avoided as a result of eliminating the use of a substrate. Material cost would be reduced as well because substrate material is no longer needed.
Circuit designers are forced in many instances to use components external to the circuit package to meet design requirements, each additional required external component adding cost, lowering reliability and causing the overall size of the electronic package to increase. These external pans must be mounted and electrically interconnected by means of technology such as a printed circuit board. If all parts are mounted within the lead frame itself the need for a printed circuit board to mount the external parts on is obviated and a manufacturing cost savings is realized. Further, a compact design is obtained by containing all components exclusively on the lead frame with no external pans, in fact, the look and feel of an IC package may be maintained, allowing the circuit package itself to be mounted directly to a pc board.
Electrical connections of external components, even on a pc board, are typically not as reliable as those made within the integrated circuit package. Overall reliability of the electrical interconnections are therefore improved by housing all the interconnections within the circuit package. Reliability of the package is also improved with regard to environmental resistance of the package. A past solution was to house a module type electronic package within a custom plastic housing. This housing is expensive to produce and has been shown to be substandard with regard to moisture resistance. Incorporating all components within the lead frame, as the present invention teaches, allows the circuit package to be encapsulated by means typically used to encapsulate an individual IC. These methods, such as potting, have proven to be very environmentally resistant.